Ž . Sensors and Actuators 77 1999 149–156 www.elsevier.nlrlocatersna Micro-stereolithography of polymeric and ceramic microstructures X. Zhang ) , X.N. Jiang, C. Sun Department of Industrial and Manufacturing Engineering, The PennsylÕania State UniÕersity, UniÕersity Park, PA 16802, USA Received 3 August 1998; accepted 16 March 1999 Abstract Ž . Micro-stereolithography mSL is a novel micro-manufacturing process which builds the truly 3D microstructures by solidifying the liquid monomer in a layer by layer fashion. In this work, an advanced mSL apparatus is designed and developed which includes an Ar q laser, the beam delivery system, computer-controlled precision x–y–z stages and CAD design tool, and in situ process monitoring systems. The 1.2 mm resolution of mSL fabrication has been achieved with this apparatus. The microtubes with high aspect ratio of 16 and real 3D microchannels and microcones are fabricated on silicon substrate. For the first time, mSL of ceramic microgears has been successfully demonstrated. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Stereolithography; MEMS; Micromachining; Microfabrication; Polymer; Ceramics 1. Introduction As an emerging technology, Micro Electro-Mechanical Ž . Systems MEMS have drawn worldwide research atten- tion in the last decade. MEMS devices have been found in many sensing applications such as airbag sensors, as well as chemical and biological sensors. In order to develop the intelligent ‘micro-system’ which is capable of both sensing and actuating, microactuators is the key to making MEMS wx a fully active device 1 . The microactuators with high output power can be achieved by using real 3D high aspect wx ratio microstructures 2 , adopting novel actuation mecha- w x nisms 1,3 , and incorporating a broader spectrum of mate- rials into MEMS such as smart ceramics and alloys beyond w x conventional materials used in IC fabrication 4–6 . Current IC-based micromachining processes used to fabricate MEMS devices have certain limitations in achiev- ing the above goals. First, most of the IC-based microma- chining processes cannot be used to fabricate complex 3D micro parts with high aspect ratios. Second, only a few semiconductors and other materials can be processed by the current IC-based micromachining for MEMS. Many other important engineering materials, such as smart ce- ramics, functional polymer, and metal alloys, cannot be directly incorporated into MEMS through the conventional IC-based micromachining processes. As an alternative, ) Corresponding author. Tel.: q1-814-863-3216; Fax: q1-814-863- 4745; E-mail: xxz10@psu.edu Ž X-ray LIGA German Lithography, electroforming and . molding process was developed to fabricate microstruc- w x tures with high aspect ratio 7,8 . However, the X-ray LIGA process has not found a large number of industrial applications due to its limited industrial accessibility and high operational cost. In addition, complex 3D structures cannot be easily achieved by LIGA process. Recently, a new three-dimensional microfabrication technique is devel- oped based on two-photon absorption with micron resolu- w x tion 9,10 . This approach provides a new way to directly write a 3D microstructure in free form. In the two-photon microfabrication, however, a short-pulsed laser with a high peak-power is required in order to achieve polymerization since the quantum efficiency is quite low. In addition, the two-photon polymerization is limited to the 3D microfabri- cation from transparent resin, since the laser beam cannot be easily focused inside of the ceramic and metal suspen- sions. A novel microfabrication process, the mSL was introduced to fabricate high aspect ratio and complex w x 3D-microstructure 11 . Sophisticated 3D parts can be made by scanning an UV beam on the liquid monomer resin, curing the resin into solid polymer layer by layer, and stacking together all layers with various contours. In contrast to conventional subtractive micromachining, the mSL is an additive process, which enables one to fabricate high aspect ratio microstructures with novel smart materi- als. The mSL process is, in principle, compatible with w x silicon processes and batch fabrication is also feasible 12 . The mSL fabrications of micropolymeric parts and subse- 0924-4247r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0924-4247 99 00189-2